The present invention relates to a paper-making press felt having good water-squeezing capability.
Conventionally, in a press part in a paper-making process, a water-squeezing operation is performed by pinching a paper-making press felt on which a wet paper sheet is placed by a pair of press rolls and by applying pressure thereto. At the nip press of the pair of press rolls, the felt is rapidly released from a press state in a region from a nip center to the delivery side of the rolls and hence expands its volume markedly. This produces a phenomenon that a large amount of water moves from fine fibers to the wet paper sheet by a capillary phenomenon in the process of volume expansion.
The phenomenon is called a re-wetting phenomenon, and is well known to a person skilled in the art. When the re-wetting phenomenon is generated, the water-squeezing efficiency is reduced at a press part, and hence various kinds of methods have been used to prevent the phenomenon.
A first method for preventing the re-wetting phenomenon was to reduce the amount of water moving to a wet paper sheet by using fibers smaller than the fibers constituting the wet paper sheet for the fibers constituting the batt layer of a felt, and the second method was to reduce the amount of water moving to the wet paper sheet by providing a felt with a hydrophilic resin layer and a hydrophobic resin layer, as disclosed in Japanese Published Unexamined Patent Application No. x2x-127590/1990.
However, the first method described above has a drawback that if the fibers of a batt layer are smaller than the pulp fibers of the wet paper sheet, a felt tends to get dirty and that fibers tend to come off markedly. Also, the second method described above has a fear that an additive or an oil component contained in the wet paper sheet will be fixed to or accumulated on the hydrophilic resin layer or the hydrophobic resin layer, or conversely, that these resin layers are melted and removed little by little, and hence has a problem that the felt can not have sufficient durability as a paper-making press felt.
The present invention has been made to solve the problems described above. It is the object of the present invention to provide a paper-making press felt which can effectively prevent a re-wetting phenomenon and can provide a user with excellent usability without using fibers smaller than the fibers constituting a wet paper sheet for the fibers forming the batt layer of a felt and without using hydrophilic resin and hydrophobic resin.
In order to accomplish the object described above, a paper-making press felt in accordance with the present invention includes a base member and at least one batt layer laminated on the base member and is characterized in that the base member is made of a plurality of ground fabrics, and in that, of the plurality of ground fabrics, a second ground fabric arranged next to a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed is a structure whose density is higher than that of the first ground fabric, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in density between them and can prevent a re-wetting phenomenon effectively.
Also, a paper-making press felt can include a base member and at least one batt layer laminated on the base member, and is characterized in that the base member has a two-layer structure of a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed and a second ground fabric arranged next to the first ground fabric, and in that the second ground fabric is a structure whose density is higher than that of the first ground fabric, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in density between them and can prevent a re-wetting phenomenon effectively in the case of the base member having the two-layer structure.
Further, a paper-making press felt can include a base member and at least one batt layer laminated on the base member, and is characterized in that the base member has a three-layer structure of a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed, a second ground fabric arranged next to the first ground fabric, and a third ground fabric arranged next to the second ground fabric, and in that the second ground fabric is a structure whose the density is higher than that of the first ground fabric, or that of the first ground fabric and that of the third ground fabric, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in density between them and can prevent a re-wetting phenomenon effectively in the case of the base member having the three-layer structure.
Still further, a paper-making press felt can include a base member and at least one batt layer laminated on the base member, and is characterized in that the base member is made of a plurality of ground fabrics and in that, of the plurality of ground fabrics, a second ground fabric arranged next to a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed is a structure whose air permeability is lower than that of the first ground fabric, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in air permeability between them and can prevent a re-wetting phenomenon effectively.
A paper-making press felt can include a base member and at least one batt layer laminated on the base member, and is characterized in that the base member has a two-layer structure of a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed and a second ground fabric arranged next to the first ground fabric, and in that the second ground fabric is a structure whose air permeability is lower than that of the first ground fabric, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in air permeability between them and can prevent a re-wetting phenomenon effectively in the case of the base member having the two-layer structure.
Still further, a paper-making press felt can include a base member and at least one butt layer laminated on the base member, and is characterized in that the base member has a three-layer structure of a first ground fabric arranged nearest to a surface on which a wet paper sheet is placed, a second ground fabric arranged next to the first ground fabric, and a third ground fabric arranged next to the second ground fabric, and in that the second ground fabric is a structure whose air permeability is lower than that of the first ground fabric, or that of the first ground fabric and that of the third, and can regulate water from moving from the second ground fabric to the first ground fabric by the difference in density between them and can prevent a re-wetting phenomenon effectively in the case of the base member having the three-layer structure ground.
Still further, a paper-making press felt can be characterized in that the first ground fabric has, or the first ground fabric and the third ground fabric have an air permeability of 50 cc/cm2 to 900 cc/cm2 and in that the second ground fabric has an air permability of 0.67 or less, which makes it possible to select the specific value of density for unerringly realizing the prevention of re-wetting phenomen.
Still further, a paper-making press felt can be characterized in that the first ground fabric is made of, or the first ground fabric and the third ground fabric and the second ground fabric are made of monofilament single yarns of 50 d to 330 d or twist yarns thereof, which makes it possible to select the specific material and the size of yarn for unerringly realizing the prevention of a re-wetting phenomenon.
Still further, a paper-making press felt can be characterized in that the second ground fabric is made of a non-woven fabric or a laminated body of non-woven fabrics, which can provide flexibility in selecting the material of the second ground fabric as long as the material selected for the second ground fabric satisfies the conditions of density and specific density, or air permeability and specific air permeability to the first ground fabric.